(1) Field of the Invention
The present invention relates to an active material for nonaqueous electrolyte battery that is used as a backup power source, and to a nonaqueous electrolyte battery containing the active material.
(2) Description of the Related Art
Conventionally, nonaqueous electrolytic solution secondary batteries such as lithium manganese dioxide batteries have been used widely as a backup power source for a mobile phone or the like. One of the characteristics of the nonaqueous electrolytic solution secondary batteries is that they have high voltage and high energy density. For example, lithium manganese dioxide batteries have charge/discharge voltage of 3 [V] or more.
Meanwhile, in recent years, mobile equipment has come to operate at low voltages in response to the demand for low power consumption. Therefore, nonaqueous electrolytic solution secondary batteries to be used as backup power sources are now required to have charge/discharge voltage of 2 [V] or less. Developed for the demand and in practical use are niobium lithium batteries in which niobium pentoxide is used as a positive electrode active material and lithium alloy is used for negative electrodes.
Niobium lithium batteries have a flat discharge voltage in a range approximately from 1.5 [V] to 1.2 [V] and enable a charging at approximately 2 [V]. Structures of such niobium lithium batteries are disclosed by, for example, Japanese Patent Application Publication No. 2002-203545 and a non-patent document, “Sanyo Lithium Battery (2004-10)”, Sanyo Electric Co., Ltd., 2004, p. 13.
However, efforts are being made to lower the voltages of mobile equipment even further. Therefore, there is a demand for nonaqueous electrolytic solution batteries that can operate at a lower voltage. For example, a nonaqueous electrolyte battery that can operate at a voltage of approximately 1.0 [V] is desired to be developed.